Did the world misjudge COVID-19 as it began its mysterious retreat?

The COVID-19 pandemic is once again on the wane, though the cause is unclear. The number of new cases in the United States dropped 35 percent in the past September, and worldwide cases have fallen by a similar amount since late August. It added that the performance was another example of a "mysterious cycle" of "outbreaks and subsides every two months" that epidemiologists have yet to provide a "sufficiently convincing explanation" for.

Whether the epidemic goes up or down depends on two things: first, the infectivity of the virus and the prevention measures taken by humans.

Let's start with the virus.

Compared with the previous two waves, the peak in August was mainly caused by the Delta variant. Delta has become the main variant in most countries, and its main feature is that it spreads faster than the original strain. The main culprit of the epidemic in Guangzhou, Nanjing, Yangzhou, Putian and Xiamen was Also Delta.

Alpha was 50 percent more infectious than the original strain, and Delta was 60 percent more infectious than Alpha. As a result, many people are concerned that the vaccine will not work against Delta. In fact, current studies show that the effectiveness of all COVID-19 vaccines against Delta is decreasing, but the decline is limited. The main problem with Delta is its high infectivity; the secondary problem is immune escape.

So the peak of the global outbreak in August was linked to a highly contagious Delta. But the other news is that because Delta is so strong, the proportion of other variants is decreasing in most parts of the world, and no variants with higher propagation power than Delta are currently seen.

Then there are the quarantine measures.

Vaccines and NPI (non-pharmaceutical interventions such as wearing masks, washing hands, social distancing, etc.) are all important to fight the pandemic. As global vaccine coverage increases, and booster shots have begun in some countries, the spread of Delta and its impact on health systems is slowing.